Mobile group II introns are retroelements that are widely hypothesized to be related to both non-LTR retrotransposons and spliceosomal introns. The overall goal of this project is to combine genetic, biochemical and structural studies to characterize the Lactococcus lactis group II intron-encoded protein (LtrA) and the pathways involved in intron mobility, particularly retrotransposition. To accomplish this, there are two specific aims. First, detailed biochemical analyses on the structural domains of LtrA will be performed. The relationship of the maturase, endonuclease, and reverse transcriptase activities to domains will be explored to understand the modular composition and evolution of LtrA. Isolated domains will also prove useful for crystallography. Second, to better understand the mechanisms of intron retrotransposition, a selectable genetic assay for isolated retrotransposition events of the group II L. lactis intron LtrB will be used. Different plasmid recipients will be employed to explore the nucleic acid targets of intron transposition and the dependency on the processes of replication and/or transcription. I will therefore understand the basic principles of group II intron biology and their relationship, as appropriate, to non-LTR retrotransposons and spliceosomal introns. [unreadable] [unreadable]